Most of my exes have been "gold star" lesbians. Of the ones that weren't, most had never had intercourse with any men. I don't think it means they're better at being lesbians or anything stupid. It's just a way of saying a lesbian who hasn't ever had sex with a man. Or alternately, a gay man who has never had sex with a woman.
Paradoxica, I don't think having never had sex with a man means you must be bi, if you've only had sex with girls and are content that way. It's the same as a straight person who's never been with someone of the same sex. For the most part, most people who've only had sex with the opposite sex are rarely challenged. If they're happy that way, they're presumed straight and everyone is usually fine with that unless they start expressing malcontent or curiousity but if a person has only been with the same sex and is happy that way, they still always get questioned how they could possibly know they don't like the opposite. Silly dual standards.